1. Field of the Invention
The present invention relates to manufacture and use of energy storing electrical components of the type referred to generically as inductors. Inductors are often used in tuned or resonant electrical circuits such as filters, oscillators or amplifiers and, in operation, convert energy in the form of electrical current flow “I” to (or from) energy in the form of a magnetic field “B” comprising closed loops of magnetic flux, as shown in FIG. 1.
2. Discussion of the Prior Art
Inductors are often used in power conversion circuits, especially in the form of transformers for Alternating Current (AC) voltage conversion and the like.
Inductors are also often used in signal dividing filters as part of loudspeaker crossover networks. Often, high power applications such as low frequency or subwoofer loudspeakers require crossover network inductors to function without saturating while passing large amounts of signal current. Coil saturation problems limit power handling and force designers to use large and expensive inductor structures.
Conventional air-core or solid-core inductors of the prior art such as the solid core inductor of FIG. 1 permit lines of magnetic flux “B” to travel through the air or any other matter which happens to be surrounding the inductor. As a result, there is uneven control over the entire flux path and so much of the flux is considered “stray”, to the detriment of the inductor's performance.
High fidelity loudspeaker systems are typically made with two or more transducers or drivers, each having a different frequency response. The division of energy between portions of the audio spectrum to each transducer is accomplished with crossover networks to achieve maximum efficiency. Crossover networks are filters that include combinations of resistors, capacitors and inductors. With the advent of high-power audio sound systems, the need for high-power handling crossover inductors has become acute. The broadband spectrum of nearly a dozen octaves exhibited by much of the music further requires crossover networks that properly direct particular segments of the audio spectrum to appropriately receptive loudspeaker drivers. Such drivers may be categorized as covering the frequency regions of contra-bass, sub-bass, bass, mid-range and high frequencies.
Because of the way the human ear responds to sound, the greatest demand for power occurs in the sub-bass and bass frequencies. In order to supply these frequencies at sufficient power levels to the appropriate driver, a crossover network needs to reject all higher frequencies without depressing the amplitude of the bass frequencies in any significant way.
Recent studies have confirmed that phasing of harmonics has a direct impact on the perception of tonal character and timbre. Further, the phase throughout the audio spectrum and wiring of electronic networks affects the sound, particularly near the bandpass extremes for each transducer of the overall sound system in which the slope of roll-off or roll-up gain contributes to the phasing well into the “flat” response region (occurring as prescribed by Bode and other researchers). The ear identifies the various harmonics or inharmonics (partials) in their relative strength throughout the ear's response spectrum developing a “formant” glossary consisting of many recipes.
The Q of an inductor provides a figure of merit as to its quality describing its loss characteristics at a specified frequency. It being frequency dependent, the Q is usually measured at 120 Hz and 1 kHz, and a measure of ohmic Direct Current Resistance (DCR) is usually also provided. The applicants have discovered that these provide an incomplete picture, however, because additional momentary characteristics or “components” are manifest that are dynamic in nature. When considered as in-series elements, Q=XL/RAC where XL is the inductive resistance and RAC is the resistance factor which includes all loss factors including the DC resistance of the winding. There is an induced series resistance RS that represents a loss or barrier to current at the specified frequency and is present as long as a signal having that frequency passes through the inductor. This resistance includes copper eddy current loss, iron eddy current loss and hysteresis loss of the magnetic material, all of which must be compensated for by the amplifier into its load. This resistance is often considered as a parallel resistance RP across the inductor and is related by the dissipation factor D where D=1/Q, since Q varies proportionately with XL which, in turn, is a function of frequency, and so it follows that RS increases with frequency.
When considering inductors for use in audio applications, this means that the bass audio output becomes depressed in the presence of a high frequency input because of an increase in RS. In other words, sound that includes a significant high frequency component leads to a rise in the “invisible” AC resistance of the inductor thereby decreasing its efficiency for as long as the high frequency signal lasts. This consideration is therefore a significant problem in broadband performance over several octaves of audio. When considered as in-parallel elements, Q=RP/XL, in a given network, the response slope is selectable in magnitude as well as frequency region. The applicants have discovered that, for example, if a 6 dB/octave roll-off could be decreased to −4 db or −5 dB/octave on its lower skirt, the result would be a noticeable improvement in tone quality (per Bode).
In the past, manufacturers have principally turned to iron lamination cores to minimize eddy current losses in the core to provide higher power handling inductors. Such cores are thought to provide low resistance with minimum number of coil turns and to provide inductors that are sufficiently efficient at utility power frequencies (50˜60 Hz), but audio frequencies typically encompass the range of 20 Hz to 20,000 Hz and higher. The high frequency content typically supplied to loudspeaker systems by digital audio components contain harmonics that were, at one time, thought to be beyond the range of human hearing. Frequencies and amplifier response above 20,000 Hz however are now recognized to affect the quality of sound sensed by the human ear. There is a need, therefore, for a new type of inductor with a high efficiency of high Q value at low frequencies, where such Q value would decrease with frequency to a lower value with increasing frequency giving noticeable sound improvement by virtue of less phase shift to upper harmonics.
The quality and definition of Audio and Video reproduction is affected by the amount of electrical noise and transient voltage spikes superimposed onto the supply line voltage. Generally the smoother the supply voltage sine-wave, the better the signal quality and definition which is translated to audio sound or video images. Electrical noise is present in the supply line voltage to audio and video equipment or other appliances and generates false data into the output signal and negatively impacts on the resultant quality. For example “Squiggles” or “fuzziness” is introduced into displayed pictures and impairs the resultant definition, and “hum”, “buzz”, “ringing” and “blurring” is introduced into the sound output similarly impairing the resultant sound definition.
Electrical noise which affects audio and video output is apparent when superimposed upon the supply voltage (sine wave). Such electrical noise can be further broken down into “Transient” noise and “Spurious” noise. Transient noise takes the form of large peaks—typically of amplitude >1% of the supply voltage. Spurious noise takes the form of a lower amplitude magnitude of less than 1% of the supply voltage. Transient and spurious noise can occur throughout the frequency spectrum. Both high and low frequency spurious noise can affect audio and video quality. High frequency spurious noise (>20 KHz) is often caused for example by other appliances and lighting fixtures powered from the same mains power supply as the audio and video equipment typically has amplitude of <1% of the supply voltage. Spurious low frequency noise (<20 KHz) is often caused by motors and generators connected to the same mains supply.
State-of-the-art power filters have a varying degree of success at filtering high frequency spurious noise. Most are unable to filter low frequency noise without the use of prohibitively expensive large value inductors and capacitors, and all are unable to filter transient noise without causing additional stress on the appliance power supply diodes. Economy generally dictates capacitive input rectification that gates in the noise on the peak portion of the line supply voltage. State-of-the-art filter networks generally have inductors and capacitors in the circuit, however these filters will usually only smooth out and suppress the relatively high frequency noise superimposed on the line voltage. The transient noise (defined as the higher power noise which exhibits higher amplitude than regular electrical noise—typically greater than 1% in relative amplitude) is superimposed upon the voltage as unwanted noise passing through traditional designs. Typical prior art filters have been limited to filtering out noise in excess of 20 KHz due to size and cost constraints associated with the larger inductors needed to effectively filter out lower frequencies. There is a need, then, for a commercially viable solution which will enable power filters and power conditioners to filter of frequencies down to 3 KHz (below which frequency the noise has little effect on picture or sound quality).
State-of-the-art power filters have another disadvantage of causing additional burden and strain on the appliance power supply diodes due to a blocking action on the needed current.
Lastly, the only way to adjust the Q value of an inductor is by selecting a different size of copper winding and/or core size thereby producing multiple inductors of the same value of inductance but with differing direct current resistance and Q values. This is both costly and inefficient. There is at present no effective way of adjusting the Q of an inductor after assembly.
There is a need, therefore, for inductive structures and methods for using inductive structures that overcome these problems.